<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
     ul{
        list-style: none;
        margin: 0;
        padding: 0;
     }
     li{
        width: 200px;
        height: 50px;

     }
     li:nth-child(1){
        background-color: red;
     }
     li:nth-child(2){
        background-color: green;
     }
     li:nth-child(3){
        background-color: ye;
     }
    </style>
</head>
<body>
   <ul>
    <li>1</li>
    <li>2</li>
    <li>3</li>
   </ul>
</body>
</html>